1. Field of the Invention
The present invention relates to a measurement method and an apparatus for measuring a focus error amount and so forth when a pattern is exposed in a lithographic process for manufacturing a semiconductor device and a display device such as a liquid crystal, and a semiconductor device manufacturing method.
2. Description of the Related Art
Recently, along with highly improving density of a semiconductor element, a pattern formed by a lithography technique shows progress in microfabrication. The finer the pattern becomes, the smaller the requirement for size uniformity becomes. As one major cause that deteriorates the size uniformity, a focus variation (focus error) of an aligner can be cited. When the focus error arises, the formed pattern varies in size, which is especially remarkable in the case of an isolated pattern and the like having small depth of focus that extremely decreases the width. For instance, it is generally said that for manufacturing a semiconductor element of 90 nm generation, a focus control at a level of ±50 nm is required.
Conventionally, the focus control in the aligner is performed in the following manner, as an example. First a sample wafer is fabricated by adopting various focus values in on-condition maintenance and the like, the width of the isolated pattern or the like is measured using a CD-SEM or so forth, and thereafter, an optimal focus value is determined by drawing a CD-focus curve. Then, the result is stored on the side of the aligner as an offset value to thereby control the focus.
Further, as another actual example of a so-called in-line focus monitor technique, the following are disclosed. In Japanese Patent Application Laid-Open No. Hei 11-186145 (Patent document 1), there is disclosed a focus variation measurement technique in which a relation between an angle of gradient of an edge and a focus position both of a resist pattern is obtained to thereby calculate a taper angle of the resist pattern formed on a wafer, so that the focus variation is measured. In Japanese Patent Application Laid-Open No. 2001-351853 (Patent document 2), there is disclosed a focus value measurement technique in which a focus value is measured by measuring a length of a resist pattern in the longitudinal direction using a dedicated mask and variation in thickness of the resist pattern.    [Patent Document 1] Japanese Patent Application Laid-Open No. Hei 11-186145    [Patent Document 2] Japanese Patent Application Laid-Open No. 2001-351853    [Patent Document 3] Japanese Patent Application Laid-Open No. Hei 8-148490
The focus control of the conventional technique requires long hours to measure a pattern size, so that the control by a time unit less than one day is difficult. Still more, it is impossible to monitor the focus variation by a time unit of several hours or less than that. In addition, in the course of a normal processing of products, no such a processing in which the focus varies in the wafer or in a lot is performed, so that a focus control using a product wafer is considered to be impossible.
Furthermore, in the in-line focus monitor technique disclosed at present, the detectable focus variation cannot satisfy a required accuracy, causing a problem that measurement repeatability and measurement accuracy are not improved in the measurement using the CD-SEM. As a consequence, a focus monitor with high accuracy is unable to be performed.